Influence of Hardener Systems and Wood on the Formaldehyde Emission from Urea-Formaldehyde Resin and Particleboards

Formaldehyde emission in the hardening process of urea-formaldehyde resin and formaldehyde emission from hardened adhesive as a function of the catalyst type were studied. In accordance with the acid type of catalyst, when using oxalic acid, aluminum sulfate, ammonium chloride and phosphate, the amount of formaldehyde released in resin hardening is practically the same. Differences are observed in the case of ammonium persulfate and hydrogen peroxide. The minimum formaldehyde release from the hardened polymer is observed when hydrogen peroxide is used and the maximum release with oxalic acid. The amount of formaldehyde released from the solidified resin decreases as the resin gelation time is increased. The use of hydrogen peroxide as the hardening catalyst leads to a reduction of formaldehyde release from the hardened resin by a factor of almost two. The amount of formaldehyde released from wood of different species was estimated as a background to the determination of particleboard toxicity. Results obtained by the iodometric method are in agreement with the content of hemicelluloses in different wood species. Wood particles were compressed under similar conditions to those maintained in the making of particleboards and the amount of formaldehyde released was determined. Formaldehyde release from finished particleboards can be due to the presence of free formaldehyde formed during urea-formaldehyde resin hardening and absorbed by wood. The absorption of formaldehyde by wood particles increases proportionally with the increase in the amount of formaldehyde being introduced.